In recent years, with spread of broadband communication services at home, also in a mobile communication system of a cellular scheme, research and development are actively conducted for the purpose of providing high-capacity data communication services. However, radio frequencies which are finite resources are running short, and it is actively studied to utilize high frequency bands and realize a high transmission rate in order to realize high-capacity data transmission.
When high frequency radio bands are utilized, a high transmission rate can be expected in a short distance, but attenuation due to a transmission distance is significant. Therefore, when high frequency radio bands are utilized in a real system, for example, the coverage area of a base station becomes small, and it is necessary to provide more base stations. Providing base stations requires significant costs, and therefore it is strongly desired to suppress an increase in the number of base stations and provide the above communication services.
Therefore, in order to make it possible even for the mobile station located outside a cellular service area to communicate with the base station, it is actively studied to make another mobile station (relay station) located between this mobile station and the base station relay the communication data. By this means, it is possible to realize communication between the mobile station located outside the cellular service area and the base station and practically expand the coverage area of the base station.
For example, Patent Document 1 discloses a radio relay scheme where a transmitting station (source), relay station and receiving station (destination), each perform a hybrid-type relay having both a channel for performing a regenerative relay and a channel for performing a non-regenerative relay. In this scheme, when a regenerative relay is performed, frame error rate performance of the receiving station become optimum.
Further, Non-Patent Document 1 discloses a technique where a plurality of relay stations relay the signals transmitted from a transmitting station and a receiving station combines the received signals which a plurality of relay stations relayed. According to this technique, the receiving station can obtain a space diversity effect by receiving a plurality of relayed signals, so that it is possible to obtain data with high accuracy. This technique is referred to as a cooperative relay scheme.    Patent Document 1: Japanese Patent Application Laid-Open No. HEI7-273707    Non-Patent Document 1: Tsuyoshi MIYANO, and others “Cooperative Relaying Technique with Space Time Block Code for Multihop Communications among Single Antenna Terminals”